1. Field of the Invention
This invention relates to a driving apparatus for a plasma display panel.
2. Description of the Related Art
A plasma display panel (designated as "PDP" hereinafter) is well known, as a display panel which relatively readily achieves a reduction in thickness and an increase in screen size. There is a need for a reduction in manufacturing cost and power consumption of the plasma display panel.
FIG. 1 is a block diagram illustrating an AC discharge type of a PDP 10, which comprises a group of X-row electrodes including X-row electrodes X.sub.1, X.sub.2, X.sub.3, . . . , X.sub.n ; a group of Y-row electrodes including Y-row electrodes Y.sub.1, Y.sub.2, Y.sub.3, . . . , Y.sub.n, each of which pairs with a corresponding one of the X-row electrodes; and a group of column electrodes including column electrodes D.sub.1, D.sub.2, D.sub.3, . . . , D.sub.m which are orthogonal to the X-row and the Y-row electrode groups. At an intersection of one column electrode and one pair of row electrodes, a discharge cell 9 filled with a discharge gas is formed for emitting light for a desired display in response to a pulse applied to the electrodes.
In the operation of the PDP 10 as described above, a scanning pulse is first applied to the X-row electrode, and a data pulse is simultaneously applied to the column electrode to perform a write discharge between the X-row electrode and the column electrode. Therefore, a sustain pulse is applied alternately to the X-row electrode and the Y-row electrode in each pair to keep light emission, so that a sustaining discharge can be maintained.
The sustaining discharge is performed by charging and discharging a static capacitance between the electrodes in the cell. The majority of the light emission of the discharge cell relies then on the sustaining discharge. For this reason, the power consumption of the entire PDP depends largely on electric power which is consumed during sustaining discharge periods. Particularly, for driving a larger-size panel, the static capacitance between the electrodes in the pair is increased, and a larger size of a driving power supply is required, which consequently leads to an increase in power consumption of the entire PDP apparatus.
To prevent increased power consumption in the PDP apparatus, a charge recovery type of driving circuit has been proposed for reducing electric power consumed for the sustaining discharge by recovering reactive power lost by a discharge during a sustaining discharge period to reuse the recovered reactive power for charging.
Referring to FIG. 2, a group of X-row electrodes X (which corresponds to the group of X-row electrodes X.sub.1 -X.sub.n of FIG. 1 connected with each other) is connected to a charge recovery type of circuit 20 for generating a sustain pulse. A driving circuit 21 for driving the Y-row electrodes includes a charge recovery type of generator for generating a sustain pulse, and another generator for generating a scanning pulse, an erasing pulse and a reset pulse as generators for producing a driving pulse (not shown).
FIG. 3 illustrates a timing chart for a sustain pulse generated by the charge recovery type of generator 20. The following description will be made for explaining a process for generating a sustain pulse during a sustaining discharge period with reference to FIGS. 2 and 3.
First, in period t.sub.1, switches SW1, SW2 and SW4 shown in FIG. 2 are turned off, while a switch SW3 of FIG. 2 is turned on. Therefore, the group of X-row electrodes has a potential level maintained at a ground (GND) level.
Next, as the switch SW3 is turned off and the switch SW1 is turned on, a discharge cell of the PDP is supplied with a charging current for a charge recovery type of capacitor C1 through a coil L1 and a diode D1 (in period t.sub.2). Subsequently, as the switch SW1 is turned off and the switch SW4 is turned on, the potential level of the group of X-row electrodes is maintained at a level of a sustain pulse voltage V.sub.D which is supplied from a power supply 22 (in period t.sub.3).
Next, as the switch SW4 is turned off and the switch SW2 is turned on, a discharging current from the discharge cell of the PDP is charged on the capacitor C1 through a coil L2 and a diode D2 (in period t.sub.4). Subsequently, as the switch SW2 is turned off and the switch SW3 is turned on, the group of X-row electrodes is maintained at the GND level (in period t.sub.5).
By repeating the foregoing operations, a series of sustain pulses can be supplied to the group of X-row electrodes. The Y-row electrode is supplied with a series of sustain pulses produced by similar operations. However, it should be understood that a generating timing for the Y-row electrode is shifted by a half cycle from that of the X-row electrode, thereby providing surface discharge between the pair of X-row electrode and Y-row electrode.
A problem arises in the conventional charge recovery type of generator for generating a sustain pulse in that such a generator tends to be short-circuited, if noise from the outside or a malfunction in a controller for controlling the switches results in generating a signal which may turn on the switch SW3 to maintain the row electrodes at the GND level in the period t.sub.3 the row electrodes are maintained at the level of the sustain pulse voltage V.sub.D.